This invention relates to non-volatile memories, such as read-only memories (ROMS), electrically programmable read-only memories (EPROMS), and electrically programmable and electrically erasable read-only memories (EEPROMS), and more particularly to improved means for generating a differential output signal in such memories.
Differential sense amplifiers for ROMS are known which sense the state of a memory cell by detecting the difference in potential between the gate of a reference transistor having a fixed reference potential and the gate of another transistor coupled to the column line of the memory cell. U.S. Pat. No. 3,938,108 discloses an example of such a differential sense amplifier. In that patent a dummy cell of the same dimensions as the memory cell and having its gate tied to a fixed voltage is used to provide the reference voltage level. The dummy cell is located outside the memory cell area. Thus, while the gate of the dummy cell is held at some fixed potential between ground and supply voltage, the gate of the transistor coupled to the column line will vary between ground and the supply voltage when the memory is accessed. Access time of 200-300 nanoseconds is asserted for the memory disclosed in the patent.